Digital output magnetoresistive (DOMR) head and methods associated therewith

ABSTRACT

A digital output magnetoresistive (&#34;DOMR&#34;) head for magnetic playback comprising one or more &#34;pinned&#34; magnetic layers having magnetic polar direction which does not rotate under an external field from the media, and a magnetic digital switching layer formed using either shape or crystalline anisotropy such that it has an easy axis parallel to the magnetic direction of the pinned layer or layers and two stable magnetization directions, parallel or antiparallel to the magnetization polar direction of the pinned layer or layers. Because of this dual stable state configuration the DOMR head produces a substantially digital output when reading magnetic information.

REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 08/239,243, filedMay 6, 1994, now U.S. Pat. No. 5,546,253.

FIELD OF THE INVENTION

The field of the invention pertains to magnetic recording, moreparticularly to a dual stable state (digital output) magnetoresistivehead for reading back magnetic information, and methods re same.

BACKGROUND OF THE INVENTION

In the past, magnetoresistive ("MR") heads and sensors have been usedfor reading magnetic information stored on both magnetic disk and tapestorage systems. Magnetoresistive heads are capable of producing highsignal output with low noise that is independent of media velocity ifthe flying height is a constant. This high signal output and low noise,i.e., high signal to noise ratio, makes possible media noise limitedoverall system performance at high areal storage densities.

Magnetoresistive heads detect magnetic transitions through theresistance change of an MR read element which varies as a function ofthe strength and direction of the magnetic flux impinging on the readelement. By applying an electrical sense current to the MR headstructure an output voltage may be generated which is proportional tothe resistance of the material, and in turn proportional to the magneticfield from the media.

A known first class of MR heads typically utilize a single-domain thinfilm (on the order of 500 angstrom units in thickness) permalloy sensorelement with a small internal crystalline anisotropy axis, or "easyaxis," typically induced during film deposition by the application of astatic magnetic field. These MR heads function according to theanisotropic magnetoresistive ("AMR") effect, where the resistance of theMR sensor element varies as a function of square of the cosine (cos²) ofthe angle between the magnetization direction of the sensor element andthe sense current direction.

Biasing techniques are typically employed with AMR heads so that the MRsensor element operates in the linear region of its transfer curve andavoids the quadratic response of the cos² function. Biasing is oftenachieved by the addition of a second permalloy layer or soft adjacentlayer ("SAL") separated by a spacer from the MR sensor element. A moredetailed description of MR heads that operate according to the AMReffect is found in "Magnetoresistive Head Technology", D. Markham etal., Proc. of the Elect. Chem. Soc. Vol. 90-8, p. 185 (1990), which isincorporated herein by reference.

Recently, a second class of MR heads, commonly referred to as spinvalves, have been developed that have a more pronounced MR effect. Spinvalve MR heads are multilayered structures that typically have two ormore magnetic layers separated by a non-magnetic layer. As discussed inU.S. Pat. No. 5,287,238 to Baumgart et at., the physical phenomenaassociated with the change in resistance of such layered magneticstructures is variously referred to as the giant magnetoresistive("GMR") effect or the "spin valve" effect. This effect has beenattributed to the spin-dependent transmission of the conductionelectrons between magnetic layers through a non-magnetic layer and theaccompanying spin-dependent scattering at the layer interfaces.

Unlike conventional AMR heads, the resistance of a spin valve MR headdoes not change as a function of applied sense current direction.Rather, as described in "Giant Magnetoresistance in Soft FerromagneticMultilayers", Dieny et al., American Physical Society Vol. 43, No. 1 p.1297 (1991), which is incorporated herein by reference in its entirety,the in-plane resistance between a pair of ferromagnetic layers separatedby a non-magnetic layer varies as a function of the cosine of the anglebetween the magnetization in the two layers.

In spin valve MR heads one or more of the magnetic layers is typically"pinned" through the use of exchange coupling, as is well known in theart, such that their magnetization direction is fixed while the MRsensor element layer is free to rotate under the influence of thefringing fields from the magnetic transitions stored on the media. Thefringing fields from the media causes the magnetization direction of thesensor element to rotate relative to the fixed magnetization directionof the pinned magnetic layer or layers. As is the case with conventionalAMR heads, spin valve MR heads having an easy axis perpendicular to themagnetic direction of the field to be sensed are known.

U.S. Pat. No. 5,159,513 to Dieny et at., and U.S. Pat. No. 5,206,590also to Dieny et at., describe a spin valve MR head consisting of amultilayered structure formed on a substrate. Both the aforementionedpatents describe a spin valve MR head having a first and second thinfilm layer of magnetic material separated by a thin film layer ofnon-magnetic material. The magnetization direction of the firstferromagnetic layer in the absence of an applied magnetic field must besubstantially perpendicular to the magnetization direction of the secondferromagnetic layer which is fixed in position.

U.S. Pat. No. 5,287,238 to Baumgart et at., describes a variation on thestructure of the spin valve MR head disclosed in the Dieny patents.Baumgart et al. discloses a dual spin valve MR head having first, secondand third ferromagnetic layers separated from each other by nonmagneticlayers. The outer ferromagnetic layers in the structure have theirmagnetic orientation fixed while the middle layer is comprised of softferromagnetic material which is free to rotate in magnetic direction incooperation with the field from the media. As in the Dieny patents, forthe described spin valve MR head to work, the magnetic direction of themiddle rotating sensor element layer in Baumgart et al. is orientedperpendicular to the magnetization direction of the fixed outer layerswhen the applied field is zero.

In these known spin valve MR heads which have only one stablemagnetization state, an analog output signal is detected by applying asmall sense current to the head structure. The voltage output is ananalog signal in that it continuously varies as a function of the MRhead's resistance. The maximum change in magnetic orientation of thesensor element layer is limited to 90 degrees from its easy axis andtypically must be constrained to even more limited rotation to providefor operation in the linear range of the MR material's transfer curve.Therefore, as such a known spin valve MR head passes over a magnetictransition on the recording media the magnetization direction of thesensor element is rotated a maximum of 90 degrees in a time varyingmanner, causing a change in resistance in the material and a resultantanalog voltage output waveform.

In order to recover the actual recorded user data this analog outputsignal is typically converted into a digital signal during thedemodulation process, which typically involves relatively complex peakdetection circuitry. In recording channels using partial responsemaximum likelihood ("PRML") detection, a Viterbi algorithm is utilizedthat is even more complex than traditional peak detection. Additionally,since in digital recording systems the user data to be stored on themagnetic media is typically written in non-return to zero ("NRZ")format, the NRZI data output of spin valve MR heads must then beconverted back to NRZ format to recover the user data.

Accordingly, it would be desirable to provide an MR head capable ofproducing a digital output in order to simplify magnetic flux transitiondetection schemes. Also, it would be desirable to eliminate the need fortransformation of the recovered data from NRZI to NRZ format.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide a digital outputmagnetoresistive head which overcomes limitations and drawbacks of theprior structures, approaches and methods.

A more specific object of the present invention is to provide a bistablemagnetoresistive data transducer head which operates in a saturationregion of the MR material's transfer curve, so as to produce a highervoltage output than conventional MR heads in response to the presence ofa proximate magnetic field.

Another object of the present invention is to provide a bistablemagnetoresistive data transducer head manifesting magnetic hysteresis soas to provide a non-return-to-zero output upon encountering a serialsequence of recorded magnetic flux regions of alternating magneticpolarity.

In accordance with principles of the invention a multilayered digitaloutput magnetoresistive ("DOMR") head provides a substantially digitaloutput for playback in magnetic data storage devices, whether disk ortape. The preferred device comprises one or more "pinned" magneticlayers. The magnetic direction or orientation of these pinned layersdoes not substantially rotate under the influence of an external fieldfrom the media. A digital magnetic switching layer is separated from thepinned layer or layers by one or more layers of nonmagnetic material.The magnetization direction of the pinned layer or layers is fixedsubstantially parallel, or antiparallel to the magnetization directionof the digital switching layer. Antiparallel, as used herein, is definedas having magnetization directions 180 degrees apart. The digitalmagnetic switching layer is formed using either shape or crystallineanisotropy such that it has an easy axis substantially parallel to themagnetic direction of the pinned layer or layers. The DOMR head has twostable states for the magnetization direction in the switching layer;parallel or antiparallel (i.e., in opposite directions), to themagnetization direction of the pinned layer(s), providing asubstantially two state or digital output according to the polarity ofthe magnetic field domains of the media.

The inventive method for reading alternating magnetic domains from arelatively moving magnetic storage media using a digital output headalso solves many of the problems encountered by methods employing analogoutput heads. Since the DOMR head operates in the saturation (nonlinear)region of the MR material's transfer curve, it is capable of producing ahigher voltage output than conventional analog output MR heads which aretypically constrained to operate in their linear region. Also, thehi-stable operation of the preferred device produces a substantially twolevel (digital) output that simplifies recording channel detectionschemes. An added benefit is that the output of the preferred device isin NRZ format, the same format typically used to record the data, ratherthan the NRZI output produced by a conventional analog read head. Sincethe output of the preferred device is in the same format as the recordeddata it is not necessary to convert the output from NRZI to NRZ as isthe case with a conventional analog output read head, thus resulting insimplification of recording channel circuitry.

In another aspect of the present invention, a method is provided fordetecting information stored upon a magnetic storage disk or tape assequential magnetic transitions. The method comprises the steps of:

(a) moving the magnetic recording disk or tape relative to a DOMR headat a predetermined relative velocity;

(b) loading a head arm assembly including the DOMR head into proximitywith the disk or tape such that the head is supported in close proximityto the recording surface;

(c) positioning the head over said magnetic transitions to be read;

(d) passing a sensing current through the head to generate a voltageacross it as a function of its electrical resistance, the resistancemanifesting a first value after the head has passed over a firstmagnetic transition comprising magnetic flux, the resistance manifestinga second value after the head has passed over a second magnetictransition comprising magnetic flux and wherein the second transitionmagnetic flux is opposite in polarity from that of the first transition;and

(e) putting out a signal proportional to the resistance to a readchannel comprising signal detection circuitry.

As a related aspect of the present invention, the method comprises thefurther step of detecting the information from the signal with thesignal detection circuitry without taking a derivative thereof.

In a further aspect of the present invention a method is provided formaking a magnetoresistive head in accordance with principles of thepresent invention. The method comprises the steps of:

(a) depositing a first layer of magnetic material on a substrate, thefirst layer of magnetic material comprising an easy axis orientedsubstantially perpendicular to a plane of a magnetic recording surfaceover which the head is to be positioned;

(b) depositing a layer of nonmagnetic material over the first layer ofmagnetic material;

(c) depositing a second layer of magnetic material over the layer ofnonmagnetic material; and,

(d) depositing an antiferromagnetic pinning layer over the second layersuch that the second layer of magnetic material has a magnetizationdirection fixed substantially parallel to the easy axis by exchangecoupling from the antiferromagnetic pinning layer.

In this aspect of the present invention, the layer of nonmagneticmaterial preferably comprises a material selected from the groupconsisting of copper, silver, gold and alloys containing copper, silveror gold; the first layer of magnetic material comprises cobalt or acobalt alloy and has an easy magnetic axis formed using crystallineanisotropy; and, the second layer of magnetic material comprises NiFe.

Further, in this aspect of the present invention the step of depositingthe first layer of magnetic material comprises the step of forming thefirst layer in a rectangular shape having a length dimension (e.g. 2.1μm) perpendicular to the plane of the magnetic recording surface overwhich the head is positioned which is approximately twice a widthdimension (e.g. 1 μm) across a recording track of the magnetic recordingsurface being followed by the head.

These and other objects, advantages, aspects and features of the presentinvention will be more fully understood and appreciated uponconsideration of the following detailed description of a preferredembodiment, presented in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Drawings:

FIG. 1A shows one stable state of the hi-stable switching operation ofthe DOMR head according to the present invention; and, FIG 1B shows theother stable state thereof.

FIGS. 2a and 2b are related graphs which show the ideal transfercharacteristics in terms of resistance vs. external magnetic field for aprior art spin valve MR head, and for the DOMR head according to theinvention, respectively.

FIG. 3A shows a first one (Case 1) of two specific embodiments of the MRdigital switching layer according to the invention; and FIG. 3B showsthe other one (Case 2) of the two embodiments.

FIG. 4a is a graph of the output of a preferred DOMR head according tothe invention as it passes over a series of magnetic transitions whenthe MR digital switching layer is shaped according to the shapeanisotropy shown in case 1 of FIG. 3.

FIG. 4b is a graph of the output of a preferred DOMR head according tothe invention as it passes over a series of magnetic transitions whenthe MR digital switching layer is shaped according to the shapeanisotropy as shown in case 2 of FIG. 3.

FIG. 5 is an exploded perspective view of an embodiment of a DOMR headaccording to the present invention.

FIG. 6 is an exploded perspective view of another embodiment of a DOMRhead according to the present invention.

FIG. 7 shows a DOMR head according to the invention as it passes over aseries of magnetically recorded transitions and a series of graphsshowing respectively, the write current used to write the input datastream, the magnetization of the medium caused by the write current, theconventional head output voltage on readback, and the output of the DOMRhead according to the present invention.

FIG. 8 illustrates a DOMR head being used in a disk drive.

FIG. 9 illustrates a DOMR head being used in a tape drive.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The operation of the bi-stable DOMR head according to the invention isshown in FIGS. 1A and 1B. The first magnetic layer 2 (layer A) has itsmagnetization direction "pinned" or fixed in the direction shown byarrow 6 such that it does not substantially rotate in magnetic directionunder the influence of fringing external fields. If the total magneticfield from other parts of the head is relatively small, MR digitalswitching layer 4 (layer B), also a magnetic layer, may be formed usingeither shape or crystalline anisotropy, as is well known in the art,such that it has a vertical easy axis that is substantially parallel tothe magnetization direction of pinned layer 2. It is of courseunderstood that any reference herein to "vertical", "horizontal","above", "below", "up", or "down" as well as to any other suchdirectional terms is relative and is merely made to assist indescribing-the relationship between various aspects of the preferredembodiments. Such terms in no way restrict the invention to thoseparticular directions.

With this perpendicular anisotropy, and vertical easy axis, themagnetization direction of the MR digital switching layer 4 can only bein one of two stable states as shown by arrow 7; it can either point up(parallel to pinned layer 2, FIG. 1A) or down (antiparallel to pinnedlayer 2, FIG. 1B, where antiparallel is defined as having magnetizationdirections 180 degrees apart, or in opposite directions) in cooperationwith the direction of the external field. Thus, as the DOMR head passesover a magnetic transition 8 in FIG. 1A the magnetic direction of MRdigital switching layer 4, as shown by arrow 7 is parallel to themagnetic direction of pinned layer 2. When the DOMR head passes over thenext magnetic transition 9 in FIG. 1B (having an opposite direction interms of magnetic flux from preceding transition 8) the magneticdirection of MR digital switching layer 4 switches states to beingantiparallel to that of pinned layer 2. The threshold level of theexternal field needed to switch the magnetization direction of MRdigital switching layer 4 from one state to the other is determined bythe digital switching layer's 4 shape or crystalline anisotropy. Aswould be obvious to those skilled in the art, the threshold will varydepending on the particular application.

The graph in FIG. 2a shows idealized transfer characteristics for aconventional spin valve MR head with resistance plotted as a function ofthe external field. In FIG. 2a it can be seen that the outputcharacteristics of the idealized conventional spin valve MR head arelinear, and no hysteresis (or magnetic memory) is displayed. Accordingto this transfer curve, as in the case of an inductive read head, theoutput of the conventional spin valve MR head is an analog waveform asis shown in FIG. 7.

The transfer characteristics for an idealized DOMR head of the presentinvention are shown in FIG. 2b. Due to the dual stable stateconfiguration, the DOMR head stays in one of the two states when theexternal proximate magnetic field is lower than the threshold. As thehead passes over a recorded magnetic flux transition from one magneticdomain to the next one having a reversed field polarity, the externalfield from the transition causes the head to switch from one state tothe other. As the media magnetic field reverses direction, as is thecase when adjacently recorded magnetic transitions are to be read, theDOMR head switches its state coordinately. If a sensing current I_(s) isapplied, the voltage level of the high and low states can be written as:

    V.sub.high =I.sub.s (R.sub.0 +ΔR), V.sub.low =I.sub.s (R.sub.0 -ΔR)

where R₀ is the resistance when the magnetization direction of the MRdigital switching layer 4 is substantially perpendicular to that of thepinned layer 2, and ΔR is the resistance change when the magnetizationdirection of the MR digital switching layer 4 is parallel, orantiparallel, as the case may be, to that of pinned layer 2, providing asubstantially digital output.

In FIGS. 3A and 3B two presently preferred embodiments of the MR digitalswitching layer according to the invention are shown. It should beunderstood that while illustrative examples are now given of using shapeanisotropy to create a vertical easy axis in the MR digital switchinglayer, that such an internal easy axis may also be created through theuse of crystalline anisotropy, as is known in the art.

In the first embodiment (case 1 of FIG. 3A) the MR digital switchinglayer has a height of 2.1 μm and a width of 1 μm, for example. Theresults of using this particular shape anisotropy are shown in FIG. 4afor a readback of an all "1"s (high frequency) pattern of magnetictransitions. As shown in FIG. 4a, the normalized output of a DOMR headhaving a digital switching layer with the shape anisotropy shown in case1 of FIG. 3A is a substantially digital waveform.

Similarly, FIG. 4b shows the output for readback of a series of isolatedmagnetic transitions for a DOMR head having its digital switching layershaped as shown in case 2 of FIG. 3B. As can be seen from a comparisonof FIGS. 4a and 4b the shape anisotropy of case 1 in FIG. 3A provides amore well defined digital output waveform than that provided with case 2of FIG. 3B.

The specific output characteristics of the DOMR head are a function ofthe particular shape or crystalline anisotropy chosen for the MR digitalswitching layer for the particular application. These factors areinterrelated and can be adjusted in combination in achieving the desiredbistable switching characteristics of the DOMR head. Other factorsincluding media magnetic remanence, media film thickness, head-to-mediadistance and MR magnetic shield structure geometries are also consideredin designing the DOMR head. From the examples provided herein, those ofordinary skill in the art will appreciate that a DOMR head with thedesired substantially digital output may be produced using a widevariety of MR digital switching layer shape and/or crystallineanisotropies.

The structure of a specific embodiment of the DOMR head according to thepresent invention is shown in FIG. 5 (and in FIG. 7). A presentlypreferred DOMR head is comprised of a series of layers typicallydeposited by thin film deposition on a suitable substrate 10 such asglass, ceramic, silicon or suitable material, for example. Depositedupon the substrate 10 is a first thin film layer of soft magneticmaterial 12, a thin film layer of nonmagnetic material 14, and a secondthin film layer of magnetic material 16. The magnetization direction ofthe second layer of magnetic material 16 is pinned in position in thedirection as shown by the arrow 22. The first layer of magnetic material12, the digital switching layer, is formed by using either shapeanisotropy (as represented in the figure) or crystalline anisotropy sothat it has an easy axis (not shown) in the vertical direction parallelto the magnetization direction of pinned layer 16 (and perpendicular tothe plane of a magnetic storage surface proximate thereto). As shown byarrow 20 the digital switching layer 12, comprises a magnetizationdirection having two stable states, parallel and antiparallel (inopposite directions) respectively, to the magnetization direction ofpinned layer 16. Digital switching layer 12 is free to switch statesfrom parallel to antiparallel and vice versa as the field from the mediagradually switches direction, as when consecutively recorded magneticdomains of alternating magnetic polarity are read.

As is known in the art, and discussed in U.S. Pat. No. 5,159,513 toDieny et al., second magnetic layer 16, the pinned layer, may be fixedin magnetic direction in several different ways. In the specificembodiment of the invention shown in FIG. 5, a thin film layer of anexchange biasing material 18 of a resistance at least several timeshigher than the material of the second magnetic layer is deposited indirect contact with the second magnetic layer 16 so that a biasing fieldcan be produced by exchange coupling. The exchange biasing thin filmlayer is typically extremely thin, such as several atomic layers inthickness (e.g. 8-10 angstroms). Layer 18 can be an antiferromagneticlayer, such as FeMn, or, alternatively, a ferromagnetic layer ofsufficiently high squareness, high coercivity and high resistance. Thestructure of FIG. 5 may also be inverted, so that layer 18 is depositedfirst, followed by layer 16, 14 and 12. Alternatively, the magnetizationof second magnetic layer 16 can be fixed in position by forming thelayer from a magnetic material having a higher coercivity (i.e.manifesting permanent magnetism) than that of the first layer ofmagnetic material 12. Use of this permanently magnetized structure wouldeliminate the need for exchange biasing layer 18.

The DOMR head is shown in another embodiment in FIG. 6. This embodimentdiffers from the embodiment shown in FIG. 5 in that it comprises first,second and third thin film layers of magnetic material, layers 24, 28and 32, respectively, deposited on a suitable substrate (not shown) suchas silicon, glass or ceramic, for example. Magnetic layers 24 and 32have their magnetization directions fixed in position in the directionas shown by arrows 34 and 38, respectively, by one of the techniquesdiscussed with reference to FIG. 5. Digital switching layer 28 isseparated from pinned layer 24 by nonmagnetic layer 26, and from pinnedlayer 32 by nonmagnetic layer 30. Digital switching layer 28 has a twostate magnetic direction, represented by dual headed arrow 36, that iseither parallel or antiparallel to the magnetic direction of pinnedlayers 24 and 32 depending on the direction of the field from the media.

Specific materials that may comprise the various layers of a spin valveMR head are disclosed in U.S. Pat. No. 5,287,238 to Baumgart et al.,U.S. Pat. No. 5,159,513 to Dieny et al., and U.S. Pat. No. 5,206,590also to Dieny et al., which are hereby incorporated by reference intheir entirety. Briefly, as with the layers described in Baumgart etal., at column 4, lines 51-59, the various layers that comprise theembodiments of the DOMR head disclosed with reference to FIGS. 5 and 6may be made as follows. The magnetic layers (pinned and switching) ofthe DOMR head may be fabricated of any suitable magnetic material suchas cobalt (Co), iron (Fe), nickel (Ni) and their alloys such asnickel-iron (NiFe), and iron-cobalt (FeCo), for example. The nonmagneticspacer layer or layers of the DOMR head may be formed as very thin filmdepositions of copper (Cu), or suitable noble metals such as silver (Ag)or gold (Au) or their alloys. The exchange biasing layer or layers ofthe DOMR head may comprise an antiferromagnetic material such asiron-manganese (FeMn) or nickel-manganese (NiMn), for example. Finally,a capping layer (not shown) of the DOMR head may be made of a materialhaving a relatively higher resistivity than the magnetic layers 28 and32, such as tantalum (Ta) or zirconium (Zr), and the capping layer maybe deposited over the top layer of the layered structure of the DOMRhead.

In FIG. 7, a playback method utilizing the DOMR head is illustrated.Write current, magnetization level of the medium, conventional headoutput, and the digital head output are plotted vs. time for anarbitrary data sequence. As can be seen from FIG. 7 the output of theDOMR head closely tracks that of the write current used to record thedata sequence. The DOMR head recovers NRZ data naturally. This cansimplify somewhat the decoding circuitry, since the data does not haveto be converted from NRZI to NRZ to recover the input data as generallyis the case with a conventional MR or inductive head. Because the DOMRhead provides a substantially digital output, demodulation schemes,i.e., peak detection can be simplified. When the DOMR head is used inconjunction with DC free codes, as are well known in the art,demodulation may be achieved simply by sampling the output signal todetermine whether it is above or below a DC level. In this case, if theDOMR head output is above the DC level, the data bit is an NRZ "1"; and,if the output is below DC level, the bit is an NRZ "0". Without DC freecodes the DC level may vary, depending upon the data being read by theDOMR head from the relatively moving medium.

In FIG. 8, an example of the use of a DOMR head in a disk driveapparatus is illustrated. The disk drive has at least one data storagedisk 100 rotating at a predetermined angular velocity in the directionof the arcuate arrow and comprising magnetic transitions stored on e.g.a multiplicity of concentric recording tracks. The disk 100 is supportedin position by a spindle which includes, or is attached to, a spinmotor, not shown, which receives control signals from the disk driveelectronics 110. Slider 102 is positioned over the magnetic recordingdisk 100, and supports one or more magnetic transducers including a DOMRhead, also not shown. The slider 102 is attached to suspension 104 whichin turn is connected to an actuator ann 106. A mechanical mover, such asa voice coil actuator 108 controls the positioning of actuator arm 106.Based on the position signals received from the disk drive electronics110, the voice coil actuator 108 moves the actuator arm 106 and hencethe slider 102 containing the DOMR head radially in and out over thedisk's 100 surface, allowing the DOMR head to be positioned over themagnetic information to be read.

As the disk 100 rotates during operation, an air beating is createdbetween the disk's 100 surface and the slider 102 such that the slider102 and hence the DOMR head "flies" over the surface of the disk 100 asit is rotated. It should be noted that the DOMR head could also be usedin a contact head application such as a "floppy" disk drive and/or amagnetic tape drive.

It will be recalled that one of the principal advantages of a DOMR headis that read channel electronics 103 may be simplified in thatsimplified serial data detection schemes may be used, since the DOMRhead recovers non-return-to zero ("NRZ") data digitally. Accordingly, aserial data stream of digital electrical signal transitions as read bythe DOMR head element of the slider 102 is conditioned and processedwithin the digital read channel 103 which "recovers" the data stream inrelation to a read data clocking signal. The serial data stream, mostpreferably in a coded format, is then passed on to the data handlingsections of the disk drive electronics, for decoding and framing intouser data blocks preparatory to delivery of the user data blocks to thehost computing system in conventional fashion. In this particularexample, the head slider 102 also most preferably comprises an inductivewrite element for writing data to selected data locations of theconcentric storage tracks. A disk drive employing conventional thin filmread/write heads which is readily adapted and improved by inclusion ofthe DOMR head of the present invention is described in commonly assignedU.S. Pat. No. 5,255,136 entitled: "High Capacity Submicro-WinchesterFixed Disk Drive", the disclosure thereof being incorporated herein byreference.

FIG. 9 illustrates the use of a DOMR head in a tape drive storagesystem. Magnetic recording tape 118 is stored on storage reel 120. Thetape 118 is passed over DOMR head structure 126 and wound onto take-upreel 122 in any conventional manner. Wheels 124 position the tapeagainst the head structure 126 such that the tape is in contact with thehead 126. The DOMR head structure 126 may comprise multiple DOMR heads;can be engaged by any conventional means; and, may comprise a contacthelical tape head, for example.

While the term "layer" is used herein to describe the switched layer,the nonmagnetic layer, and the pinned layer, those skilled in the artwill appreciate and understand that a particular layer may be formed asa series of depositions of suitable materials, and that such series mayhave a variety of planar shapes and thicknesses.

Having thus described an embodiment of the invention, it will now beappreciated that the objects of the invention have been fully achieved,and it will be understood by those skilled in the art that many changesin construction and widely differing embodiments and applications of theinvention will suggest themselves without departing from the spirit andscope of the invention. The disclosure and the description herein arepurely illustrative and are not intended to be in any sense limiting.

What is claimed is:
 1. A mass storage device comprising:a magneticrecording medium comprising magnetic transitions stored thereon; amagnetoresistive head supported in close proximity to said recordingmedia comprising a layered structure deposited on a substrate, saidlayered structure comprising a pinned layer of magnetic material and adigital switching layer of magnetic material separated by a layer ofnonmagnetic material, said pinned layer having a substantially fixedmagnetization direction, said digital switching layer comprising firstand second magnetization directions, said first magnetization directionbeing substantially parallel to said magnetization direction of saidpinned layer after said head passes a first magnetic transition definedon the recording media, and said second magnetization direction beingsubstantially antiparallel to said magnetization direction of saidpinned layer after said head passes a subsequent magnetic transitiondefined on the recording media and manifesting a magnetic field polarityopposite in direction to that of said first magnetic transition; anddigital read channel electronics having an input connected to the headfor receiving and processing a serial data stream put out by the headduring relative movement between the magnetic recording medium and thehead.
 2. The mass storage device of claim 1 wherein an output from thehead from its movement relative to said magnetic recording medium is afunction of the strength and direction of said magnetic flux from saidmagnetic domains being read and comprises a substantially digitalwaveform.
 3. The mass storage device of claim 2 wherein saidsubstantially digital waveform put out by the head follows anon-return-to-zero format.
 4. The mass storage device of claim 1 whereina mechanism for switching magnetization direction of said digitalswitching layer comprises shape anisotropy and wherein said digitalswitching layer comprises a rectangular shape having a length dimensionsubstantially perpendicular to the medium which is approximately twice awidth dimension thereof.
 5. The mass storage device of claim 1 wherein amechanism for switching magnetization direction of said digitalswitching layer comprises crystalline anisotropy and wherein saiddigital switching layer of said head comprises an easy axis formed usingcrystalline anisotropy.
 6. The mass storage device of claim 1 whereinsaid mass storage device is a disk drive and said magnetic recordingmedium is a rotating magnetic data storage disk.
 7. The mass storagedevice of claim 1 wherein the head includes a pinning layer formedadjacent to the pinned layer on the other side of the nonmagnetic layer,for fixing the direction of magnetization of said pinned layer.
 8. Themass storage device of claim 1 wherein the layer of nonmagnetic materialcomprises a thin film not substantially greater than several atomicthicknesses of a material selected from the group consisting of copper,silver, gold, and alloys including copper, silver or gold.